


The Demon Plague

by castielrisingabove



Category: Supernatural
Genre: AU, Alternate Universe - Medieval, boyking, demon
Language: English
Status: Completed
Published: 2015-02-14
Updated: 2015-02-14
Packaged: 2018-03-12 20:56:02
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 2,231
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3354998
Author URL: https://archiveofourown.org/users/castielrisingabove/pseuds/castielrisingabove
Summary: <blockquote class="userstuff">
              <p>A Medieval AU. Castiel, a light mage fallen from the Higher Power, has teamed up with a Knight, Dean Winchester, and his brother Sam, who is a dark mage. Usually, they avoid the Higher Power of the Kingdom and fight off forces of evil, but everything has come to a stop with the appearance of the Demon Plague. Sent by the Dark Order, a group of dark mages, it corrupts the mind of anyone infected. While they become powerful, they are also filled with blood lust and darkness. When both Sam and Dean fall ill to the plague, Castiel has a choice: kill them, or try to find an impossible cure.</p>
            </blockquote>





	The Demon Plague

He couldn't believe he hadn't noticed. Sure, Dean had been a bit more reckless, but Castiel had assumed it was just because he was nervous. The demon plague, after all, was slowly plunging the Kingdom into anarchy. First it was Dean's increase of violence, then it was Sam's sudden coldness. Cas should have caught on sooner. It was not until he caught Dean drinking the blood of their latest enemy that Cas knew something was wrong...but then it was too late. The last thing he remembered was Dean's fist to his face.

Cas awoke to the taste of blood on his lips. "Rise and shine," Sam said, kissing Castiel again. Groaning, Cas opened his eyes to find Sam standing over him, blood on his lips as he stroked Cas' chest. Looking down, Cas realized he was restrained by ropes. It was then the events of the previous night came rushing back. And if Dean was infected...

"What happened?" Cas croaked, though he didn't want to hear the answer.

"It was Dean," Sam replied, breaking into an uncharacteristically dark grin, "He helped me see the way...and now I'm powerful beyond measure." 

Dean wandered into the tent, placing a hand on Sam's shoulder. "Careful, Sammy," he said, smirking as Sam nuzzled his skin, "You know you can't turn a light mage. He could be dangerous."

Sam pouted. "But he's mine," he said, fingers absentmindedly caressing Cas' chest, "I want him."

Ah. It suddenly became very clear why Dean hadn't ended Castiel's life when he had the chance. Somehow, although all other traces of humanity appeared to have been lost, the Winchesters were still loyal to each other. And if Sam wanted Cas alive, Dean wasn't about to go take that away from him. As the Winchesters talked, Cas' mind raced. What was he supposed to do? There was no cure to the demon plague, not that anyone knew. He could try and escape, the ropes would be easy enough to break, but that still left the Winchesters at large. Which meant death was their only option...but Cas couldn't bring himself, not even in imagination, to end their lives.

There had to be a cure, Cas thought desperately as he looked into the unfamiliar eyes of men he once considered family. If the demon plague came from the Dark Order...perhaps it came from their top mage. Lucifer. Castiel shivered. He'd heard the stories. Once, Lucifer had been part of the Higher Power, until he corrupted his magic and left, creating his own faction bent on world domination. And with this plague, they were coming close. Their forces were growing every day as more succumbed. Those who did not join simply created anarchy and fear, which the Dark Order fed off of. Lucifer was terrifying, but...

"C'mon, Castiel," Sam crooned, pulling Castiel back into the current conversation, "You promise to stay with us, and we'll let you out of these ropes. It'll be like nothing changed..."

"Unless you double cross us," Dean interjected a twisted smile crossing his face, "Then I'll make sure you know what we're capable of."

Cas glared, closing his eyes as Sam came in closer, pressing kisses to his jaw. "I'd listen to him," Sam murmured, "My brother, like me, is stronger than beyond belief. I don't want him to hurt you, but..." he pulled away, shrugging, "I can't always control him."

"Stop," Cas breathed through clenched teeth. He wasn't even sure if he'd be able to get the Winchesters back, the last thing Castiel wanted was for Sam's shadow to touch him. Sam pulled away, looking hurt. "You're not you."

Sam scrambled to his feet, confused. "But...but I am! Castiel, I've just become a better version of myself." He leaned into Dean, wrapping his arms around his brother for comfort. Dean growled at Cas.

"Take it back," he snarled, "Sam has finally become everything he ever wanted."

Cas shook his head, "Sam has become a monster."

Sam gasped, burying his head in Dean's shoulder. Dean pressed a kiss to Sam's head. "Why don't you take a break, Sammy?" he murmured, "Drink some blood to keep up your strength. I'll set this guy straight." Sam nodded, leaving the tent without a second glance. With Sam gone, Dean hardened. "You made the wrong move this time, Castiel..." he growled, moving in on Cas, blade drawn.

With a burst of magic, Cas broke the ropes, stumbling to his feet. Another shot of magic was used to temporarily daze Dean, and Cas was out of the tent, sprinting away from the campsite. 

***********

It didn't take much to make it to the headquarters of the Dark Order. Light mages were in short supply and since they couldn't be turned, often they were captured, brought to the Dark Order under the promise that if they swore allegiance, they could live. It was there Castiel met Lucifer for the first time. The man, though he did not stand out physically, emanated a great amount of power. With his shirt off, Cas could see the wings, not unlike the same ones he had tattooed to his own back, branded onto Lucifer's shoulder blades. Castiel was roughly pushed into the room and he stumbled to the feet of Lucifer.

"Brother," Lucifer said softly, reaching down a hand to help Cas up. Castiel refused, pushing to his feet. "I'm so glad you could come..."

"I haven't come to join," Cas replied, "I've come to save my friends."

Lucifer smiled sadly. "You mean the Winchesters," he said, snapping his fingers. A cloud appeared, and inside the cloud were images...Dean massacring villagers, drinking their blood. Men, women, children, none were spared. And when the village had been ravaged, Dean helped Sam atop a throne of corpses, Sam surveying the few trembling survivors with a dark smile on his face, Dean by his side...

"He's promising," Lucifer said, "When he finds me, when I train him...he'll become unstoppable. My heir apparent."

"No!" Cas said sharply, pulling out of the cloud, which evaporated, "No, please...I'll do anything..."

Lucifer paused thoughtfully. "A light mage willing to give so much for the fallen...don't you know I am unstoppable?"

"There must be a way," Cas insisted, "I'll do anything."

"Everything I want is within my grasp," Lucifer replied pacing the floor, before stopping. "But it interests me that a mere pion thinks he could rival my power..." he whirled around on Cas. Lucifer's followers watched with bated breath. "Very well. You and I will go to the Winchesters. I will offer power, you will offer the cure. We'll see who makes it through..." Rummaging into his pocket, he withdrew a small vial, tossing it to Castiel.

************

With a snap of his fingers, Lucifer brought both he and Castiel back to the Winchesters, who were still basking in the glory of defeating the village. As the Winchesters realized the company they were in, Dean bowed low. Sam, on the other hand, merely nodded his head. "What brings the great dark lord to our humble realm?" he asked obsequiously. 

Lucifer stepped forwards, prodding Cas towards the Winchesters. "I have come with an offer of power," Lucifer said, making an incision on his arm. His blood dripped black onto the dusty road. "He has come with a supposed cure." Lucifer gestured to Cas, smiling. "It is up to you to choose."

Sam stood, putting a hand on Dean's chest to restrain him. "After me, my knight," he purred, stepping towards Lucifer, eyes shining with admiration. In a moment of panic, Cas stepped between them. 

"Wait!" Cas cried, knowing if Sam drank, he would never be the same. He looked to Dean, who had pulled out a blade and begun to advance on Cas, "Tell me this Sam is the same one you used to know...that he treats you like a brother and not a servant...and I won't stand in your way."

Dean stopped, a look of confusion seeping into his gaze as he looked to Sam and back. "I protect my brother..."

"But is that him? Will that be him, once he's gotten all the power he could comprehend?"

Dean looked even more worried as Sam turned, placing a gentle hand to his face. "Don't stand in my way," Sam cooed, "Don't you want this? With this power, I'd have everything I wanted..." Dean frowned, pulling away from Sam and advancing on Lucifer.

"I want my brother back," Dean growled, pointing the blade at the Dark One. 

Lucifer smiled sadly, "Oh, Sam. I'm sorry your brother has betrayed you. But I'm offering you a new family...with you as my prince, heir to the throne..."

"NO!" Dean and Cas cried out at once as Sam knelt, lapping the blood off Lucifer's arm. As he turned to face them, his eyes were black.

"Give me the cure," Dean said, teeth gritted, "If I'm going to die, I want to at least die human." Cas obliged and Dean took a sip, body glowing for a moment before he collapsed.

"What did you do to him?" Cas shouted, rounding on Lucifer. 

Lucifer shrugged, "In becoming human, he's lost most of his strength. Dean will probably take a day or so to recover. Or he would...if he survived." He turned to Sam, placing a hand on his shoulder. "My son, they have betrayed you. You ought to punish them..."

Sam turned to look at Cas, a hint of worry crossing his face. "Him?"

Lucifer nodded. "You must be strong...command respect..."

Sam swallowed, then nodded, his face steeling as he amassed a dark energy.

"Sam?" Cas asked tentatively, "Sam, please?"

But it was for naught. Sam blasted, sending Cas through the wall of a nearby house. He hit the ground, hard, fighting to push to standing. "Sam, please!" Cas begged, but another blast sent him down, this time for good. 

Sam strode in, pulling a blade as he examined Cas. "You will not betray me again," he said, though his voice was stiff. And then he was on the ground next to Cas, carving into him, smiling through Cas' screams. When he was done, Cas was almost unconscious, his skin flayed as he inhaled and exhaled weakly. "It's a shame," Sam said, "You were supposed to be mine." He leaned down, pressing one final kiss to Cas' bloody lips.

Light burst from Cas' chest, spreading into Sam, who screamed in agony. As the light faded, Sam's eyes had returned to his normal color. He blinked, disoriented, as he stared first at Cas, and then at his own bloody hands. "C-Cas?" Sam asked, voice trembling.

Cas knew that voice. It held none of the cold, calculating malice of one corrupted with darkness. He heaved a sigh, body relaxing as he closed his eyes. "Sam...you're okay..."

He had no time to explain further, though, as Lucifer strode into the room. "You might have won this," Lucifer said with a snarl, "But just because you've saved your friends doesn't mean you're saving the world. I will win. And Sam will be mine." With a snap of his fingers, he was gone. Cas succumbed to his injuries, becoming unconscious.

**************

It had been difficult for Sam, trying to care for his brother and Cas while still reeling from the loss of power himself. Dean awoke to help not long after, but Cas... "He'll pull through," Dean said, trying to coax a worried Sam to sleep, "The little guy's always pulled through."

And he did, though he was still weak. "I think we've found a cure," Cas confided in Dean that night, "The blood of a light mage...we've got an in..." While Dean and Cas discussed plans for the future, for saving the Kingdom and stopping the Dark Order, Sam kept his distance, ashamed of what he'd done. Still, Sam couldn't help but wander past the tent often, trying his best to furtively check in on the light mage. 

"Sam?" Cas called out, stopping the other man in his tracks, "I, uh...I missed you..." Outside the tent, Sam fell to his knees, tears streaming down his face. It took coaxing from both Dean and Cas to get Sam to enter the tent, encouraged by the promise they could all sleep inside together for the night. It would be like the old days, Dean insisted, and reluctantly, Sam agreed.

It was his first time around Cas since the incident. Both Sam and Dean lay curled protectively near Cas, Dean filling most of the conversation before falling asleep. When he did, Cas turned to Sam. "I told him I'd do anything, you know," Cas murmured, reaching out a hand to give Sam's shoulder a weak squeeze, "He underestimated us, huh?" Sam smiled hesitantly, curling in a little closer as Cas pressed a kiss to his forehead. 

"Cas?" Sam whispered, "I'm so sorry...I shouldn't have...I..."

"I love you..." Cas mumbled, before falling asleep himself. Sam watched for a moment, amazed that he could be so calm about the incident, but something about Cas' demeanor, something about how safe Sam felt next to the two most important people in his life, gave Sam the first moment of hope since falling sick with the demon plague. With a small smile, Sam too fell asleep, reassured that come whatever, they were facing the challenge of saving the world together.


End file.
